1. Field of the Invention
The present invention relates to treating articles with reactive spray and, more specifically, to an apparatus and method for etching or otherwise chemically treating electronic printed circuit board substrates.
2. Prior Art
The art is replete with various disclosures of apparatus and methods of etching printed circuit board substrates. "Handbook of Printed Circuit Manufacturing" by Raymond H. Clark, 1985 Van Nostrand Reinhold Co., Inc., pp 396-416, discloses etching in detail. "Printed Circuits Handbook", second edition, by Clyde F. Coombs, Jr., 1979 McGraw-Hill, Inc. pp 8-8:8-45 also disclose etching. One type of etching technique is called spray etching. Spray etching techniques include single or double sided etching with either horizontal or vertical positioning of the printed circuit board substrate. In single side horizontal etchinq, it is known that spraying etchant upward onto a substrate can be used for producing very fine line work. There also exist automatic horizontal etching machines such as disclosed in U.S. Pat. Nos. 4,781,205; 4,190,481 and 3,935,041.
Various problems exist in the spray etching technology. Generally, uneven etching can result when both sides of a double sided printed circuit board substrate are etched simultaneously in either a horizontal or vertical spray etcher. In the vertical system, etching solution can run down the board causing uneven etching activity from the top of the board to the bottom. With the horizontal system, puddling of etchant can occur on the top side of the board causing different etching activity than on the bottom side. This problem has become more important as finer line geometries have been developed particularly in the range of line widths under 10 mils wide and, more particularly, to very fine line etching below 5 mils in line width.
It is therefore an objective of the present invention to provide an apparatus and method for etching printed circuit board panels with a substantially reduced risk of uneven etching.
It is another objective of the present invention to provide spray etching for very fine line etching.
It is another objective of the present invention to provide single side spray etching which can etch very fine lines on a first side of a printed circuit board panel, but can protect the panel's opposite second side from contact with the etchant.
It is another objective of the present invention to provide a means for preventing etchant sprayed upwardly against printed circuit board panels from dislodging or moving the panels upward away from the support conveyed.
It is another objective of the present invention to provide a mechanism according to the present invention that can be installed or adapted for use in horizontal spray etchers known in the art.
It is another objective of the present invention to provide a mechanism according to the present invention that can relatively easily be removed from and installed in sprayer apparatus.
It is another objective of the present invention to provide a mechanism according to the present invention that can provide a temporary mask for a whole side of an article being sprayed that can travel at the same speed as an article conveyor to prevent damage to the article being conveyed.
It is another objective of the present invention to provide a mechanism according to the present invention that can allow fine line etching of thin copper with relatively little undercut.